Improving color of iron stained material



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Patented Sept. 17, 1940 UNITED STATES IMPROVING COLOR OF IRON STAINEDMATERIAL Sidney D. Wells, Combined Locks, Wis., assignor to The DowChemical Company, Midland, Mich., a corporation of Michigan No Drawing.Application May 6, 1939, Serial No. 272,142

8 Claims.

This invention relates to the color lightening and brightening ofmaterials occurring naturally and contaminated with iron, manufacturedin contact with iron, or otherwise subject to contamination with ironwhereby the material contains iron compounds discoloring the material.As such materials are mentioned paper pulps, clay, kaolin, fine sand,bauxite, and the like, old newspapers, and in fact any material whichcan be formed into an aqueous suspension and treated in the presence ofwater, such as paper stock, straw, and other materials.

The invention will be particularly described as it relates to thetreatment of a paper pulp, but this is only by way of example, and notby way of limitation as to broad features of the invention. However,because of the presence of tannin in paper pulp, the invention ispeculiarly applicable to color lightening of such pulps.

Paper made from pulp containing small amounts of iron compounds derivedfrom the vegetable materials of which the pulp is comprised, from thewater or from chemicals used in the production thereof, has a dull shadewhich is objectionable in many kinds of paper. This dull shade I havefound is imparted to the paper by the iron compounds and may be of anorange or reddish cast. Where tannic acid is present in even a slightamount and comes into contact with the pulp, the color imparted to thepulp is grey and produces a marked lowering of the brightness of thefinished product.

In accordance with the present invention, the color of the pulp can bebrightened materially even though compounds of iron may be present inamounts sufficient to seriously dull the color of the pulp if made bythe usual processes. This is obtained by changing the iron compounds toferrous ferricyanide, commonly known as Turnbulls Blue. When this isaccomplished, the color characteristics of the paper is materiallyimproved, for the grey compounds and other compounds which wouldotherwise absorb the blue components of the light reflected from thesurface of the fibers are converted into compounds which do not absorbthe blue components, whereby the paper appears to be whiter in color.Since the reflected light is usually more deficient in blue than inyellow and red, the general effect is to raise the whiteness of thereflected light, and consequently the brightness of the color. Inordinary practice the excess of red and green is corrected by addingblue dye or pigment and the degree of whiteness is usually broughtsomewhat lower than the parts blue in the pulp mixture as furnished. Bychanging the iron compounds over to Turnbulls Blue they are changed fromcompounds which absorb the blue components of white light to one whichreflects them very effectively and the result is an increase in theamount of blue reflected. By the control of the amount of Turnbulls Blueproduced, the red and yellow components of the light reflected are onlyabsorbed to the extent to which they exceed the blue. As a consequence,the general effect produced is an increase in whiteness.

In practicing this invention, the pulp is first subject to a treatmentwhereby the iron compounds present are reduced to the ferrous state,after which the pulp is reacted with a small amount of a ferricyanide.Any one of the usual reducing agents can be employed, such as sodium,potassium, and ammonium hydrosulfites. I can also employ successfullysodium, potassium and ammonium addition products of a hydrosullite andan aldehyde, or a ketone, such as is disclosed in the Hirschkind Patent2,071,305 of February 16, 1937. I can also successfully employ thesodium, potassium, and ammonium sulfoxylates and other sulfoxylates,such as those disclosed in the Hirschkind Patent 2,071,306 of February16, 1937. I can also successfully employ any of the above compoundsmanufactured in situ, and I have operated with particular success byemploying zinc dust in connection with sulfurous acid or bisulfites ofsulfuric acid present in the pulp or other suspension. Zinc hydrosulfitecan be manufactured in situ, or added, or any reducing agent can be usedwhich is sufficiently rapid in reducing action to permit the process tobe practiced without any extensive change in the procedure and equipmentof the industry in which the color brightening is being practiced. Forthe purposes of illustrating the process, the following examples aregiven on paper pulps.

Time of reaction: Three hours at room temperature.

Brightness: Raised from 63 to 70%.

The brightened pulp was used with sulphite pulp in the manufacture ofprint papers.

till

Pounds action of a reducing agent effective toreduce sub- 2. Unbleachedsulphite pulp %0 stantially all iron therein to the ferrous state,Spruce groundwood 800 and adding a ferricyanide to said suspension afterClay 300 said reduction to react with the ferrous iron and Rosin size 5form Turnbulls Blue in said solid. Paper blue R .007 3. A process forimproving the color of a finely Rhodamine .047 divided material darkenedby the presence of Alum 10 iron or iron compounds, the processcomprising Zinc hydrosulphite 7 subjecting an aqueous suspension of saidmate- Potassium ferricyanide 2 rial to the reducing action of a reducingagent The ingredients listed were added to the beater in the orderindicated and no more time was taken with each beater so charged thanwas taken by the same treatment prior to the use of the brighteningagents. The color of the paper made by this process was as bright aspaper made with 250 pounds of bleached sulphite and 750 pounds sprucegroundwood with a considerable saving in cost.

Groundwood pulps, unbleached hemlock sulphite, and bleached soda pulpsare all considerably improved in brightness by this process oftreatment. Unbleached spruce sulphite and. bleached kraft pulps are alsoimproved as well as unbleached kraft pulps when made into paper in whichblue dye is ordinarily used as part of the color.

The conditions described in the foregoing description and examples aretypical but the present process is not limited to the particular casescited and can be extended or modified to: suit numerous conditions.

In the treatment of other materials such as those previously mentioned,the material to be treated is disintegrated and then treated with thereducing agent in an amount sufiicient to reduce the iron to the ferrousstate. Thereafter the material is treated with the ferricyanide, all thewhile in a water suspension or in the presence of water. The pH of theaqueous suspension is adjusted and maintained at that most favorable toaction of the reducing agent employed. The temperature of the suspensioncan also be raised by heating to- F. and as high as 212 F. if desired.

This is a continuation in part of my application Serial Number 163,857filed September 14, 1937 and allowed November 7, 1938 but now forfeited.

I claim:

1. A process for improving color of a material darkened by presence ofiron or iron compounds comprising subjecting the material in an aqueoussuspension to the reducing action of a reducing agent to reducesubstantially all iron present to the ferrous state and reacting thereduced iron with a ferricyanide.

2. A process for improving color of a finely divided solid contaminatedwith iron or iron compounds comprising forming a suspension of saidsolid in water, subjecting said suspension to the effective to reducesubstantially all iron present to the ferrous state and reacting the soreduced iron with a ferricyanide to form Turnbulls Blue in saidsuspension.

4. A process for improving the color of a mineral material darkened bythe presence of iron or iron compounds, the process comprising reducingsubstantially all iron in said material while said material is in finelydivided form and in an aqueous suspension with a reducing agent and thenreacting said reduced iron with a ferricyanide to'forrn Turnbulls Bluein said material.

5. A process for improving the color of a cellulose pulp darkened by thepresence of iron or iron compounds, the process comp-rising reducingsubstantially all iron in said pulp in aqueous suspension with ahydrosulfite and then reacting said reduced iron with a ferricyanide toform- Turnbulls Blue in said pulp, said hydrosulfite being employed .inan amount of about 1% on the Weight of the pulp present, saidferricyanide being present in an amount of about 0.25% on the weight ofpulp present.

6- A process for improving the color of a cellulose pulp darkened by thepresence of iron or iron compounds, the process comprising subjecting anaqueous suspension of said pulp to the reducing action of a reducingagent effective to reduce substantially all iron present to the ferrousstate and reacting the so reduced iron with a ferricyanide.

7. A process for improving the color of a cellulose pulp darkened by thepresence of iron or iron compounds, the process comprising subjecting anaqueous suspension of said pulp to the reducing action of a hydrosulfitefor about half an hour to reduce substantially all iron present to theferrous state and reacting the so reduced iron with an alkali metal saltincluding, upon hydrolysis, the ion Fe(CN)e.

. 8. A process for improving the color of a cellulose pulp darkened bythe presence of iron or iron compounds, the process comprisingsubjecting an aqueous suspension of said pulp to the reducing action ofa hydrosulfite for about half an hour to reduce substantially all ironpresent to the ferrous state and reacting the so reduced iron with amaterial providing the ion Fe(CN)c to react with said ferrous iron.

SIDNEY D. WELLS.

